A so-called separate function type electrophotographic photoreceptor has a photosensitive layer composed of a charge generating layer capable of generating a charge carrier on light irradiation and a charge transporting layer into which the thus generated charge carrier can be efficiently introduced and which is capable of efficiently moving the thus generated charge carrier. In recent years, an amorphous silicon type electrophotographic photoreceptor having a charge generating layer made of amorphous silicon and a charge transporting layer made of an amorphous material which is formed by a plasma CVD method has been attracting attention because it has a possibility of basically improving charging properties and productivity of conventional amorphous silicon type photoreceptors without impairing excellent characteristics possessed by amorphous silicon, such as photosensitivity, high hardness, and heat stability and is therefore promising for obtaining electrical stability on repeated use and a long working life. Attention being paid on these aspects, amorphous silicon type electrophotographic photoreceptors using various charge transporting layers have been proposed. For example, a charge transporting layer which can be used in such an amorphous silicon type electrophotographic photoreceptor of separate function type includes a layer comprising silicon oxide or amorphous carbon formed by a plasma CVD method as disclosed, e.g., in U.S. Pat. No. 4,634,648.
In the above-described amorphous silicon type electrophotographic photoreceptor of separate function type, improvement in chargeability and reduction in dark decay can be brought about by using amorphous silicon as a charge generating layer and using, as a charge transporting layer, a substance having a smaller dielectric constant and higher resistance than the amorphous silicon. However, since a film formed by the above-mentioned plasma CVD method has the same rate of film formation as an amorphous type film and also has a complicated layer structure, the probability of film defects increases to reduce productivity of a photoreceptor, resulting in an extreme increase of production cost.